astrophysics
23 posts — page 2
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Noise in spectra and map domain
Spectra NET or $\sigma$ is the standard deviation of the noise, measured in mK/sqrt(Hz), typical values for microwave amplifiers are 0.2-5. This is the natural unit of the amplitude spectra (ASD), therefore the high frequency tail of the ASD should get to the expected value of the NET.
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Interactive 3D plot of a sky map
update May 2024: See the new version of this tutorial Mayavi is a Python package from Enthought for 3D visualization, here a simple example of creating a 3D interactive map starting from a HEALPix pixelization sky map:
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Elliptic beams, FWHM and ellipticity
The relationship between the Full Width Half Max, FWHM (min, max, and average) and the ellipticity is: FWHM = sqrt(FWHMmin FWHMmax) e = FWHMmax/FWHMmin
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pyfits memory leak in new_table
I found a memory leakage issue in pyfits.newtable, data were NOT deleted when the table was deleted, I prepared a test on github, using objgraph , which shows that data are still in memory: https://gist.github.com/884298 the issue was solved by Erik Bray of STSCI on March 28th, 2011 , see bug report: http://trac6.assem
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healpix coordinates
Healpix considers latitude theta from 0 on north pole to pi south pole, so the conversion is: theta = pi/2 - latitude longitude and phi instead are consistently from 0 to 2pi with zero on vernal equinox (for ecliptic ). zero in the direction from Sun to galactic center (for galactic )
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Decibels, dB and dBm, in terms of Power and Amplitude
It's not difficult, just always having some doubts... Power $latex L{dB} = 10 log{10} \left( \dfrac{P1}{P0} \right) $ 10 dB increase for a factor 10 increase in the ratio 3 dB = doubling 40 dB = 10000 times Amplitude $latex L{dB} = 10 log{10} \left( \dfrac{A1^2}{A0^2} \right) = 20 log{10} \left( \dfrac{A1}{A0} \right)
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Relation between Power density and temperature in an antenna
Considering an antenna placed inside a blackbody enclosure at temperature T, the power received per unit bandwidth is: $latex \omega = kT$ where k is Boltzmann constant.
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pillole di astrofisica
curiosita' ben spiegate da annibale d'ercole, interessante l'idea di avere un livello base e un livello avanzato http://www.bo.astro.it/sait/spigolature/spigostart.html